Several subsets of B-ALL cells have activated BTK, but only pre-BCR⁺ ALL cells are sensitive to ibrutinib. (A) pBTK and total BTK expression in ALL cell lines. (B) Proliferation/viability of different ALL cell lines after ibrutinib treatment as measured by XTT assay. Displayed are the mean with 95% CI from at least 3 independent experiments. (C-D) Comparison of viable cell counts (C) and percentage of viable ALL cells (D) after 96 hours of treatment with 1 µM of ibrutinib. Results were normalized to DMSO-treated controls and are presented as the mean with 95% CI from 3 independent experiments. ns, not significant. *P < .05; **P < .01; ***P < .001; ****P < .0001.